1. Field of the Invention
The present invention relates to a rotary connector which is mounted on a steering shaft of an automobile or the like and performs an electric connection between electric devices provided to a steering wheel and a car body respectively.
2. Description of the Prior Art
Conventionally, there has been proposed a rotary connector which electrically connects an electric device provided to a steering wheel with an electric device provided to a car body.
This rotary connector enables the electric connection between the electric device which is provided to the steering wheel which constitutes a rotary body and the electric device which is provided to the car body which constitutes a fixed body. The rotary connector accommodates a flexible electric cable or an optical fiber cable (these are generally referred to as xe2x80x9cflexible cablexe2x80x9d hereinafter) in a wound form between a rotor portion which is rotatably driven by the steering wheel and a case which constitutes a stator portion. The flexible cable has one end thereof fixedly secured to the rotor portion and the other end thereof fixedly secured to the stator portion. Due to such a constitution, the rotary connector enables the electric connection between respective electric devices by making use of the reeling and unreeling of the flexible cable.
A conventional rotary connector is explained in conjunction with attached drawings.
FIG. 4 is a cross-sectional view showing the conventional rotary connector and FIG. 5 is an enlarged cross-sectional view of a portion B of FIG. 4.
As shown in FIG. 4, this rotary connector 100 is generally comprised of a pair of upper-side first rotor member 11 and a lower-side second rotor member 12 which are concentrically and rotatably connected to each other, a cable accommodating portion 13, rollers 14, a roller holder 15, a lower cover 16, and a flexible cable 17 which is accommodated and wound in the inside of a space defined by the first and second rotor member 11, 12, the cable accommodating portion 13 and the cover 16.
Here, the first rotor member 11 and the second rotor member 12 are united to form a movable housing, while the cable accommodating portion 13 and the cover 16 are united to form a fixed housing. Further, they are constituted such that when the movable-side housing is rotated in the clockwise direction or counter clockwise direction, the winding of the flexible cable 17 in the space is tightened or loosened.
In the rotary connector 100 having such a general constitution, the fixed-side housing is fixedly secured to a car body (not shown in the drawing) and the movable-side housing is fixedly secured to a hub (not shown in the drawing) of a steering shaft. At the same time, by connecting both ends of the flexible cable 17 respectively to electric devices at the car body side and the steering wheel side by way of respective connectors (not shown in the drawing), the rotary connector 100 can be used as electric connection means of an airbag system, a horn circuit or the like mounted on a vehicle.
Further, the first rotor member 11 includes a cylindrical portion 11a having an approximately circular cylindrical shape and an annular notched portion 11b which is formed in an outer peripheral portion of one end of the cylindrical portion 11a. 
The second rotor member 12 includes a large-diameter cylindrical portion 12a having an approximately circular cylindrical shape, an intermediate-diameter cylindrical portion 12b which is contiguously connected to the large-diameter cylindrical portion 12a, a small-diameter cylindrical portion 12c which is contiguously connected to the intermediate-diameter cylindrical portion 12b, and an annular holding portion 12d which is formed perpendicularly in the radial direction from a joining portion of the large-diameter cylindrical portion 12a and the intermediate-diameter cylindrical portion 12b. 
This large-diameter cylindrical portion 12a of the second rotor member 12 is made to pass through the cylindrical portion 11a of the first rotor member 11 and the second rotor member 12 is engaged with the first rotor member 11 by means of a suitable means such as a snap-in joint, for example. Then, by arranging an upper surface of the holding portion 12d of the second rotor member 12 and the notched portion 11b of the first rotor member 11 such that they are brought into contact with each other, a groove-like space portion 11c is formed.
The cable accommodating portion 13 includes an annular side wall 13a and has both end portions opened.
The roller holder 15 includes a planar annular base portion 15a and a plurality of roller supporting portions 15b which are perpendicularly and outwardly protruding from the base portion 15a. This roller holder 15 is arranged in the inside of the cable accommodating portion 13. Further, the roller holder 15 makes a portion of the inner peripheral side of the base portion 15a thereof arranged in the inside of the abovementioned space portion 11c. 
The cover 16 includes an approximately planar annular wall portion 16a, a side wall 16b which is perpendicularly formed on the outer peripheral portion of the wall portion 16a, and a stepped portion 16c which is protruded in an L-shaped cross section inwardly from the inner peripheral portion of the wall portion 16a. Further, the side wall 13a of the cable accommodating portion 13 is engaged with the side wall 16b of the cover 16 by a suitable means such as a snap-in joint, for example, so that the cable accommodating portion 13 and the cover 16 are united to form the fixed housing.
Further, the cover 16 makes a portion of the inner peripheral side of the stepped portion 16c thereof arranged in the inside of the abovementioned space portion 11c. The portion of the inner peripheral side of the abovementioned base portion 15a of the abovementioned roller holder 15 and the stepped portion 16c of the cover 16 are laminated to each other and are arranged in a loose state with a play.
Here, the portion of the inner peripheral side of the base portion 15a, the stepped portion 16c and the holding portion 12d are arranged such that they face the notched portion 11b of the first rotor member 11 in an opposed manner, while the portion of the inner peripheral side of the base portion 15a and the stepped portion 16c are arranged in the inside of the notched portion 11b. In this manner, the portion of the inner peripheral side of the base portion 15a, the stepped portion 16c and the holding portion 12d are laminated and arranged in three layers. Then, an outer surface of the holding portion 12d and an outer surface of the wall portion 16a of the cover 16 are arranged on an approximately coplanar plane. In this state, with the provision of the holding portion 12d, the base portion 15a and the stepped portion 16c are formed such that they are not disengaged from the notched portion 11b.
Here, assume the thickness size from the outer surface of the holding portion 12d to the inner surface of the base portion 15a of the roller holder 15 as a size L2 (see FIG. 5), this size L2 becomes a relatively large thickness size because of the laminated structure in three layers.
The flexible cable 17 is a strip-like body which is formed by extending a plurality of conductive bodies made of copper (Cu) or the like on one surface of a base film made of an insulation tape, for example. The number of conductive bodies of this strip-like body is set to a given number corresponding to the number of circuits of electric devices to be connected.
The flexible cable 17 has both end portions thereof electrically led out to the outside of the movable-side and fixed-side housings. Further, the flexible cable 17 is placed on the base portion 15a of the roller holder 15 such that the flexible cable 17 can be reeled and unreeled.
As mentioned above, in the conventional rotary connector, the portion of the inner peripheral side of the base portion 15a, the stepped portion 16c and the holding portion 12d are sequentially laminated and arranged in three layers such that they face the notched portion lib of the first rotor member 11b. Accordingly, the thickness size of this portion becomes large and hence, the thickness of the rotary connector in the axial direction becomes large whereby there has been a problem that it becomes impossible to make the rotary connector thin.
Further, recently, there has been a tendency that the number of circuits of electric devices connected by way of the rotary connector 100 is increased. Further, there has also been a tendency that the size of the flexible case 17 in the widthwise direction becomes physically large corresponding to the increase of the number of the circuits. In the rotary connector 100 which accommodates the flexible cable 17 which has the large size in the widthwise direction, although there has been a tendency that the thickness in the axial direction becomes large, there is a demand for making the rotary connector 100 thin on the other hand.
The present invention has been made to solve the abovementioned problems, and it is an object of the present invention to provide a rotary connector which can largely increase the height of a space which accommodates a flexible cable without increasing the height of the rotary connector.
To achieve the abovementioned objects, according to the present invention, there is provided a rotary connector comprising a fixed housing having an outer cylindrical body and a bottom plate which is protruded inwardly from an outer periphery of a lower end of the outer cylindrical body, a movable housing being rotatably engaged with the fixed housing and having an inner cylindrical body which forms an accommodating space between the inner cylindrical body and the fixed housing, a top plate formed on at least either one of the housings such that the top plate suppresses the downward movement of the movable housing to the fixed housing, a flexible cable being accommodated in the accommodating space, being wound and being electrically led out to the outside of the fixed housing and the movable housing, and a hollow movable body being rotatably arranged in the accommodating space and having reverse rotation portions which reverse the rotating direction of the flexible cable, wherein a support cylindrical body which has a diameter smaller than an outer diameter of the inner cylindrical body and forms a stepped portion between the support cylindrical body and the inner cylindrical body is integrally connected to the inner cylindrical body at a lower portion of the inner cylindrical body, an engaging portion which is rotatably engaged with the movable body is protruded downwardly from a peripheral portion of a bottom surface of the inner cylindrical body at the stepped portion, an inner peripheral portion of the bottom plate of the fixed housing is bent toward a bottom surface of the inner cylindrical body at a position inside the engaging portion and is extended along the bottom surface of the inner cylindrical body so as to form a bent portion, and a holding portion which rotatably sandwiches the inner peripheral portion of the bottom plate of the fixed housing between the holding portion and the bottom surface of the inner cylindrical body is protruded outwardly from an outer peripheral portion of a lower end of the support cylindrical body.
Due to such a constitution, it becomes possible to provide the rotary connector which can largely increase the height of the space in which the flexible cable is accommodated without increasing the height of the rotary connector.
Further, according to the rotary connector of the present invention, the engaging portion may have a height size approximately equal to a thickness size of the movable body.
Due to such a constitution, the play of the movable body can be easily reduced with a simple constitution.
Further, according to the rotary connector of the present invention, between the inner peripheral portion of the bottom plate of the fixed housing and the bottom surface of the inner cylindrical body of the movable housing as well as between the inner peripheral portion of the bottom plate of the fixed housing and the holding portion of the support cylindrical body, gaps which allow the rotation of the movable housing relative to the fixed housing may be formed.
Due to such a constitution, it becomes possible to rotate the movable housing in a stable state.
Still further, according to the rotary connector of the present invention, the top plate is integrally formed with the inner cylindrical body, a top plate stepped portion is formed on an outer peripheral portion of a bottom surface of the top plate, and an engaging portion which is engaged with the top plate stepped portion is protruded inwardly from the outer cylindrical body of the fixed housing.
Due to such a constitution, the inner cylindrical body and the outer cylindrical body can be surely engaged with each other.